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Definitions
A caster is usually measured by the size of its wheel. For example, a 3" caster
would have a 3" wheel -- even though the total overall height of the unit is more
than 3" tall. Casters come in two basic types: Swivel and rigid. Some manufacturers
also call the rigid "fixed" or "stationary" -- which is not a good term for something
that is supposed to move. Casters are mounted using fastenings -- usually a
plate that is bolted or welded in place, or a stem that is inserted into tubing.
Axle. The bolt that runs through the wheel and through the swivel (a.k.a. "kingpin.").
Bearing. A bearing is the moving part that allows the caster to move. It refers to both
the swivel bearing (a.k.a. raceway), and wheel bearing.
Bolt Holes. The holes in the top plate allowing the caster to be mounted on the cart.
Bore. The hole through the middle of a wheel. Also a very tedious person.
Brake. Just like the emergency brake on a car -- when applied, it helps prevent the wheel
from rolling.
Capacity. Also known as load capacity -- the weight the caster will safely hold.
Caster. A wheel on a swivel, attached under a piece of furniture or other heavy object to
make it easier to move. (The dictionary came up with this definition, not us.)
Diameter. The wheel diameter of a caster.
Fastening. The method of mounting a caster to the furniture or cart (i.e., top plate,
threaded stem, etc.).
Hub. The center core of a wheel.
Hub Length. The length of the bore of a wheel. The hub length is usually wider than the
tread.
Kingpin. The axle that holds the fastening to the caster body and allows the unit to
swivel.
Load Capacity. Also known as capacity -- the weight the caster will safely hold.
Overall Height. The total vertical height of the caster, from the floor to the top of the
mounting plate, or the base of the stem.
Rigid. A caster that doesn't swivel, but still rolls forward and back. Also known as a
"fixed" or "stationary" caster.
Stem. A fastening that usually fits into tubing for the caster to be mounted.
Swivel Lock. Just like it sounds: It locks the swivel, making the caster act as a rigid.
Swivel Raceway. One or two rows of ball bearings which bear the weight of the caster and allow
the unit to swivel.
Swivel Radius. The horizontal distance from the center of the kingpin to the trailing edge of the
wheel. This determines the "sweep" of a caster as it pivots -- a good thing to know to make sure the
wheel doesn't strike something as it turns.
Thread Guard. A small piece of metal or plastic that fits over the wheel bearing to help prevent
threads, dirt, and other materials from getting into the wheel. Note the spelling -- thread guard, not
tread. Big difference.
Tread. The part of the wheel that rolls on the ground. Not to be confused with "thread".
Tread Width. The width of the wheel tread.